1. Field of the Invention
The invention relates to electrical connections, in particular the use of composite materials to make such connections.
2. Discussion of the Related Art
Recently, there has been a desire to find alternatives for the traditional soldering methods of making electrical connections. This desire has arisen from the need to simplify large-scale commercial processes, as well as to provide temporary, but reliable, electrical contacts, such as used for testing purposes. Several alternatives have been found in the area of composite materials. Some composite materials have utilized wire segments in a non-conductive matrix. Other composite materials have utilized spherical particles, held in a non-conductive matrix, as a bridge between adjacent electrical contacts. See, e.g., U.S. Pat. No. 4,737,112.
Additional composite interconnection media have been developed in sheet form, with the sheets exhibiting anisotropic, z-direction electrical conductivity (where the z-direction is across the thickness of the sheet and the x- and y-directions are in the plane of the sheet.) See, e.g., U.S. Pat. Nos. 5,522,962, 5,045,249, and 4,118,102, the disclosures of which are hereby incorporated by reference, Jin et al., "New, z-direction anisotropically conductive composites," J. Appl. Phys., Vol. 64, No. 10, 1988, and Jin et al., "Optically Transparent, Electrically Conductive Composite Medium," Science, Vol. 255, 1992. The anisotropic conductivity is provided by individual chains of electrically conductive particles reaching across the thickness of the sheet, as illustrated in FIG. 1. The conductive particles 100 are typically magnetic and therefore capable of being aligned in z-direction chains by application of a magnetic field during the curing of a matrix material 102. The matrix 102 is generally an elastomeric material, which makes it possible to compress the sheet between two electrical components 104, 106 such that a desired electrical connection is made between contact pads 108, 110 of the components.
The long-term reliability of these composite interconnection media has been a concern, however, and improved media which address this concern are desired.